What is tuberculosis (TB) infection?

TB infection is detected by the administration of a tuberculin skin test on the arm. A single needle is used to put some testing material, called tuberculin, under the skin. In two or three days, a nurse or a doctor will check to see if there is a reaction to the test. The test is "positive" if a bump about the size of a pencil eraser or bigger appears on the arm. This bump means a person probably has a TB infection. 

A chest X-ray is done to see if someone with a positive skin test (TB infection) also has TB disease.


People who are infected with TB do not feel sick, do not have any symptoms, have a normal chest X-ray, and cannot spread TB. However, they may develop TB disease at some time in the future. People with TB infection but are not yet sick can take medicine so that they will never develop TB disease.

Show All Answers

1. What is tuberculosis?
2. What are the symptoms of tuberculosis (TB)?
3. How is tuberculosis (TB) spread?
4. What happens if I have a positive skin test?
5. What will happen on my first visit?
6. What if I am diagnosed with tuberculosis (TB)?
7. How Is tuberculosis (TB) disease treated?
8. What is Directly Observed Therapy (DOT)?
9. What Is Multidrug-Resistant Tuberculosis (MDR TB)?
10. What is tuberculosis (TB) infection?
11. How can a person get tested for tuberculosis (TB)?
12. What if a person has been vaccinated with BCG?
13. What people with tuberculosis (TB) infection are at risk of developing TB disease?
14. How is tuberculosis (TB) infection treated?
15. What if a person has HIV infection?